First, welcome to 3FC and congratulations on your 40+ pounds lost!! What a wonderful accomplishment!
When it comes to your weight goal the most important thing is how YOU feel about it. The smaller you become the more noticiable 5 and 10 pounds lost is going to be. So going from 171 to 155 is going to make a HUGE difference in how you look.
My advice to you is to keep it at 155 and reevaluate your final goal as you get closer. Get to 160 and see how you feel.